Field of Invention
The present invention relates to a rare earth permanent magnet field, and more particularly to a NdFeB magnet containing cerium and a manufacturing method thereof
Description of Related Arts
Due to excellent magnetic performance, the rare earth permanent magnet material gets more and more applications, and is widely applied to nuclear magnetic resonance imaging, computer hard disk drive, sound system, mobile phone and so on. With the energy-saving and low-carbon economy requirements, the NdFeB rare earth permanent magnet material is further applied in fields of automobile part, household appliance, energy-saving and control motor, hybrid electric vehicle, and wind power generation.
In 1983, Japanese Patents No. 1,622,492 and No. 2,137,496 firstly disclosed the NdFeB rare earth permanent magnet material and characteristics, compositions and manufacturing methods thereof. U.S. Pat. Nos. 6,461,565, 6,491,765, 6,537,385, 6,527,874 and 5,645,651 also disclosed manufacturing methods of the NdFeB rare earth permanent magnet material.
Currently, the high-performance rare earth permanent magnet material is generally used to prepare the rare earth permanent alloy through the vacuum melting rapid-solidifying method. In the existing vacuum melting rapid-solidifying process, the rapid-solidifying alloy raw materials including pure iron, ferro-boron, rare earth materials and other additive metals are sent to the crucible to melt for once, so that during the melting process, the rare earth and other more expensive raw materials may be volatilized and lost; in addition, the raw materials are put into the crucible under atmospheric environment, so that the rare earth materials are oxidized, thus increasing the slags during the melting process. The above factors affect the utilization rate of the heavy metal materials, causing the waste to a certain degree. The vacuum melting rapid-solidifying furnace, produced by Japanese ULVAC, adopts the design of secondary feeding, but the object is to fill the loading space from raw material melting in the crucible during the melting, so as to increase the furnace installed capacity, which is not able to resolve the loss of the heavy metal materials at high temperature and serious slags while melting the rare earth materials.
In the manufacturing process of the NdFeB rare earth permanent magnet device, NdFeB raw materials are generally molten to form the alloy, and then the NdFeB alloy is sintered to form the NdFeB block through powder metallurgy method, and then the NdFeB block is machined to form devices with various shapes. Because NdFeB is hard and brittle, in the machining process, a large number of corner wastes are produced. In addition, with the passage of time, some mechanical devices which use NdFeB rare earth permanent magnet are not used again due to failure, life expectancy and other reasons, many scrapped NdFeB permanent magnets are able to be recovered. Due to high material cost of the rare earth permanent magnet materials, methods for recycling rare earth permanent substandard products, waste materials and scrapped NdFeB permanent magnets are always researched and studied in the industry, so as to reduce the raw material cost of the rare earth permanent materials and save the existing natural resources. Due to high oxidation degree of the rare earth permanent waste materials, if these waste materials are molten and used again as the melting raw materials, a large number of slags are produced during the melting process, which results in the limitation of the re-melting process of the waste materials to be unable to be widely applied. Therefore, Japanese related companies commonly adopt the non-remelting process to recycle the rare earth permanent waste materials. For example, ZL 99800997.0 and U.S. Pat. No. 6,149,861 disclosed a method for recycling sintered NdFeB waste materials, in which the waste materials are ground, acid washed and dried, and the product is subjected to calcium reduction treatment, so as to obtain reusable raw material alloy powders, and then other alloy powders are added into the powders for adjusting the composition thereof, to further manufacture the sintered NdFeB permanent magnet material. ZL 02800504.X and U.S. Pat. No. 7,056,393 disclosed a method of using a sintered NdFeB substandard product, in which the sintered NdFeB substandard product is coarsely pulverized by a hydrogen crushing process and then made into fine powders, the fine powders made from the normal raw material are mixed with the fine powers made from the substandard product, and then the sintered NdFeB permanent magnet is manufactured. The above-mentioned method of using non-remelting waste materials is not only complicated in procedure, but also needs to prepare alloy powders with different compositions to adjust components and improve the sintering capacity thereof, which inconveniences the production process. More importantly, in the waste utilization method, due to the non-remelting, the powders made from the waste materials has high contents of oxygen and other impurities, so that the magnetic properties of the manufactured rare earth permanent magnet material are seriously affected.
With the development of NdFeB rare earth permanent magnet, the amount of praseodymium neodymium is increased, the amount of lanthanum cerium is decreased, to ensure the rare earth balance application, it is very important to research NdFeB which is added with lanthanum cerium. Because the added lanthanum cerium obviously decreases the coercive force of the magnet, how to improve the coercive force of the magnet containing lanthanum cerium becomes a very important issue.